1. Field of the Invention
The present invention relates to a control system for reading out a program in a more preferable state from a plural memories stores the program used for causing an electronic apparatus to be operated processing, to an electronic apparatus therefor, and to a recording device wherein the plural memories are included.
2. Related Background Art
Conventionaly, within the semiconductor storage device field, the use has been proposed of a variety of memory devices (hereafter referred to as memories). Included in these proposed memories are various semiconductor devices, such as mask ROMs, EPROMs, EEPROMs and flash memories.
For instance, since for microcomputers used for controlling electronic apparatuses such as cameras, compact size and the frugal use of space are prerequisites, one-chip microcomputers for which memory and peripheral devices are mounted on a single chip are frequently employed. Recently, since the sizes of programs and the data memory capacities have been increased as the functions provided for cameras have become more varied and enhancements have been added, electrically rewritable memories having large capacities are demanded, and one-chip microcomputers that incorporate electrically rewritable flash memories, as well as mask ROMs and RAMs, have gradually come to be employed.
As an example, proposed is a system wherein a program for operating a microcomputer is stored in a read only memory (a mask ROM) and is executed to operate the microcomputer, or a system wherein such a program is stored in an electrically rewritable read only memory so as to cope with a bug in the program.
In addition, also proposed is a microcomputer that includes an electrically rewritable read only memory and a read only memory. In this case, parameters for individual controllers are stored in the rewritable memory, i.e., parameters are stored that are obtained by adjusting variances in manufacturing procedures and individual performances, so that individual products can be provided for which the performances are uniform with little manufacturing variances.
A camera system using multiple memories, including a flash memory, is actually disclosed in Japanese Patent Application Laid-Open No. 2000-89090. This system employs a flash memory and an EEPROM, and a large amount of data for which rewriting is not required, or is seldom required is stored in the flash memory, while a small amount of data for which rewriting is frequently performed is stored in the EEPROM. In this manner, the multiple memories can be employed efficiently without reducing their service lives. Also disclosed in U.S. Pat. No. 5,678,082 is a system wherein a flash memory is divided into multiple blocks, and means for rewriting data only in a specified block is provided. In this manner, a program can be easily changed without requiring the rewriting of the contents in all the areas of the flash memory. Furthermore, disclosed in Japanese Patent Application Laid-Open No. 6-168599 is a configuration wherein a flash memory and a mask ROM are employed (overall, the configuration is regarded as a virtual flash memory) and wherein data that will not be rewritten are stored in the mask ROM and data that can be rewritten are stored in the flash memory. In this manner, an inexpensive flash memory is provided for which the writing time is reduced. And proposed in U.S. Pat. No. 5,565,957 is a camera comprising switching means for, only during the writing process, rendering a flash memory conductive by supplying writing power.
However, all of these conventional examples are provided in accordance with the writing characteristic of nonvolatile memory, and while memory types are devised that depend on the data to be written or on the size of a program, in no proposal are there included other memory characteristics, such as an operating voltage (=operating current consumption) and an operating frequency. Especially for battery operated apparatuses, such as cameras, an often repeated request is for the provision of efficient control for their operation, and the reduction, to the extent possible, of their consumption of power.
Furthermore, in the above conventional examples, no consideration is given to the use of power control for executing a control program stored in flash memory. And while after the flash memory is rendered conductive a constant rising time is required before the reading and writing enabled state is reached, no consideration is given in the conventional examples to the falling time for the conductive memory. It is expected that flash memory will be used as electrically rewritable memory having a large capacity; however, for a battery-operated apparatus, such as a camera, the level of current consumed by flash memory is such that a conductive state can not be constantly maintained, and thus, from a viewer's perspective, the consumption of power must be reduced as much as possible. Whereas, an increase in operating speed is also required to improve usability and to reduce a release time lag, and the control provided for a camera must be optimized in order that low current consumption can be implemented while there is no deterioration of the usability.
In addition, according to the above conventional examples, in a case wherein control programs for the individual functions of a camera are to be stored in memories and wherein there is a memory switch each time there is a change to a different function, when before and after a memory change the operating voltage or the operating frequency differ greatly, time is required to reach a voltage or a frequency that can adequately support the operation of the selected memory. In some cases, when a memory change occurs while the voltage or the frequency is still within a range wherein the operation is disabled, an erroneous camera operation will occur. Since especially for such camera functions as a strobe function and an autofocusing function for which there is a large difference in the operating voltage or the frequency, when a change is made from the strobe operation, for which the voltage drops greatly, to the autofocusing function, for which a fast operation is required, a failure in the operating sequence of the camera will occur. However, while in the conventional examples consideration is given to the size of the data that is to be employed, the data rewriting speed, the size of the memory and the data contents to be written, no consideration is given to the operating conditions for the individual memories that are to be employed. Therefore, control of the memories must be exercised under power conditions that ensure all the memories can be employed, and the efficiency with which this control is exercised is not always adequate for an apparatus, such as a camera, that uses a battery. Thus, when a predetermined camera operation is performed for which the power voltage drops precipitously, a power state will exist wherein the operation of a specific memory is guaranteed while the operation of another memory is not. In this case, so long as the camera operation can be performed only by the operation of the memory that is guaranteed, the camera can be operated at a lower voltage. However, for a system, such as an inexpensive compact camera for which a battery voltage is directly supplied to power a microcomputer, it is demanded that a stable camera operation be guaranteed even when the power source voltage is lowered.